1. Field of the Invention
The present invention relates to a method and related apparatus for improving Discontinuous Downlink Reception (DRX) operation for a user equipment (UE) in a wireless communications system, and more particularly, to a method and related apparatus for stopping a timer when the UE leaves a specific radio resource control state, for improving DRX operation.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system, the Universal Mobile Telecommunications System (UMTS), has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS (Quality of Service) requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. In addition, the 3rd Generation Partnership Project (3GPP) has set forth Long Term Evolution (LTE) with addition of new functions to provide packet-switching-domain-only services.
According to the related protocol specifications, one of protocol stacks of the UMTS, access stratum (AS), can be segmented into sub-layers for different functions. The operations of the sub-layers in the AS are well known in the art, and detailed description is not given here. The Radio Resource Control (RRC) layer, a Layer 3 protocol, is the core of communications protocols related to AS and is located in radio network controllers (RNC) of the UMTS Terrestrial Radio Access Network (UTRAN) and a user equipment (UE). The RRC layer uses RRC messages to perform RRC procedures. The RRC layer defines various RRC states to describe the usage of radio resource for the UE. RRC states can be divided into idle mode and RRC connected mode according to whether the RRC connection is established. RRC connected mode are further divided into CELL_DCH state, CELL_FACH state, CELL_PCH state and URA_PCH state.
The RRC layer in the UE starts different timers respectively according to RRC procedures, RRC messages, and initiation or transition of RRC states. One of the timers, a timer T319, is started when the UE enters the CELL_PCH state or the URA_PCH state and is stopped when the UE initiates a cell update procedure or a URA update procedure. On the other hand, a Discontinuous Reception (DRX) operation is configured by the RNC and allows the UE to restrict the downlink reception times in order to reduce power consumption. When the DRX operation is enabled, the UE is only required to receive physical downlink channels by a specific cycle. In HSPA system, only one DRX scheme is configured and a related DRX cycle length coefficient is used to determine a DRX cycle accordingly.
Furthermore, 3GPP Release 7 introduces a second DRX scheme for the CELL_PCH state and the URA_PCH state that is intended to allow fast paging after state transition to the CELL_PCH state or the URA_PCH state. When the UE enters the CELL_PCH state or the URA_PCH state, a new timer T319 is started and the DRX cycle based on the first DRX cycle length coefficient, as mentioned above, is used for paging reception. When the timer T319 expires, the UE changes to use the DRX cycle based on the second DRX cycle length coefficient. For further information about the second DRX scheme, please refer to 3GPP TSG-RAN WG2 #58 R2-072262.
Note that, the timer T319 is started when the UE enters the CELL_PCH state or the URA_PCH state. So the timer T319 is only applicable for UEs in CELL_PCH and URA_PCH state and should be stopped when the UE leaves the CELL_PCH state or the URA_PCH state. Furthermore, it is possible that the UE may leave CELL_PCH or URA_PCH state without initiating the cell update procedure. For example, a UE in the CELL_PCH state with a dedicated HS-DSCH Radio Network Temporary Identifier (H-RNTI) being configured can move to the CELL_FACH state due to uplink data transmission without initiating the cell update procedure. As a result, stopping the timer T319 only when the UE initiates the cell update procedure or the URA update procedure does not cover all conditions of state transition of the CELL_PCH state or the URA_PCH state.